Reclaimed rubber



' istics.

Patented Dec. 8, 1942 z,cl,551

RECLAIMED RUBBER Paul J. Dasher, Akron, Ohio, assignor to The B. F.Goodrich Company, New York, N. Y., a corporation of New York No Drawing.Application November 1, 1939, Serial No. 302,368

18 Claims.

This invention relates to reclaimed rubber and has as its principalobjects to provide an improved method for reclaiming soft-vulcanizedrubber and to provide a reclaimed rubber closely approximating naturalcrude rubber in properties.

Due to the fact that reclaimed rubber is extensively used in themanufacture of many types of rubber articles, the reclaiming ofvulcanized rubber has become one of the most important units of themodern rubber industry. Up to the present time the most widely usedmethods of reclaiming soft-vulcanized rubber have been the so-calledacid method and the alkali method in which scrap vulcanized rubber isheated in the presence of an acid solution, or in the presence of analkali solution, as the case may be. The reclaimed rubber produced bythese and other known reclaiming methods is, however, by no meansequivalent to the original crude rubber but differs from it in manyimportant respects. For example, difierences are evident in' the millingand processing properties, in the tack, in solubility in the ordinaryrubber solvents, in ouring properties, and in similar physicalcharacter- Summing unit may be said that ordinary reclaimed rubber, aspreviously prepared, is merely plasticized vulcanized rubber. When thisordinary reclaimed rubber is mixed with solid 'crude rubber, aheterogeneous mixture is produced in which'the reclaimed rubber is inthe form of discrete particles that are clearly discernible' bymicroscopic examination as being entirely distinct and separate from thesolid crude rubber. Ordinary reclaimed rubber will not dissolve in thecommon rubber solvents merely by contact with-the solvent andconsequently does notidry 'to.,.a"smooth,' homogeneous, and" tackyUnlike solid crude rubber,freshly cut surfaces of ordinary reclaimedrubber cannot be pressed back together to form a tight-bond.

I have discovered a method of reclaiming softvulcanized solid rubberthat produces a plastic,

. claimed rubber can be brokendown ona mill in much the same way thatsolid crude rubber is broken down. It dissolves in the ordinary rubbersolvents, merely by contact with the solvent, to

.product acement that dries to a homogeneous tacky film. This reclaimedrubber blends perfectlywith solid crude rubber and produces ahomogeneous product, with no discrete particles of the reclaimed rubberevident when examined under a microscope. Freshly cut surfaces of thisnew reclaimed rubber will form a tightly adhesive bond when merelypressed together. This new reclaimed rubber is not merely plasticizedvulcanized rubber but is definitely a homogeneous material quite similarto milled natural crude rubber.

The reclaimed rubber of this invention can be blended with new cruderubber in substantial percentages for the manufacture of high qualityrubber products. For example, tire treads may have incorporated in themconsiderable percentages of reclaimed rubber prepared according to thepresent invention and such treads resist wear equally as well as thosemade entirely from new crude rubber. This new reclaimed rubber can alsobe compounded with compounding ingredients in much the same way as cruderubber and can be vulcanized to form superior rubber articles. It can bemolded, extruded and fabricated in any of the well known methods thatare employed by the rubber industry and, in fact, may be used for anypurpose for which prior reclaimed rubbers have been used.

To prepare the reclaimed rubber of the present invention I assocaitesoft-vulcanized solid rubber, preferably in a finely-divided condition,with an aliphatic mercapto amine having the general formula A-R-Nstituents other than hydroxyl groups, mercapto groups and amino groups;Y is X or OH; A is a radical including a mercapto sulfur atom attacheddirectly to R. and with the remaining valence of the mercapto sulfursatisfied by a hydrogen atom or a hydrocarbon nucleus. After associatingthe vulcanized rubber with a mercapto amine the mixture is heated untilthe rubber becomes plastic, which ordinarily requires a heatingcomparable to the heating times and conditions now customarily employedin the acid and alkali reclaiming process. The resulting plastic massmay then be washed with water in order to remove any particles of fabricor other extraneous material that may have been present in the originalvulcanized rubber scrap. The reclaimed rubber is then dried andthereupon is ready to be used like any solid crude rubber or ordinaryreclaimed rubber in the preparation and manufacture of rubber articlesor for other uses to which such materials have been subjected.

Typical examples of the above mentioned mercapto amines are thealkanethiol amines including the ethanethiol amines such as Z-aminoethanethiol, diethanethiol amine, and mercapto ethyl ethylene diamine;and the propanethiol amines such as 3-amino propanethiol, 1,3-diaminopropanethiol, tri-isopropanethiol amine, di-isopropanethiol amine,isopropanethiol amine, Z-methyl Z-amino propanethiol, and l-aminopropanethiol. Other examples are the alkanedithiol amines such as thepropanedithiol amines: Z-amino 2-methyl propanedithiol-l,3,1-(N,N-diamylamino) propanedithiol-1,3, 2-amino propanedithio1-1,3, and B-aminopropanedithiol-1,2. Further examples of the aliphatic mercapto aminesutilized in this invention occur with an aryl group replacing a hydrogenon the amino nitrogen. This is exemplified by such compounds as phenyldiethanethiol amine, and phenyl ethanethiol amine. Still otherreclaiming agents may be prepared by substituting a hydrocarbon nucleusfor the hydrogen on the mercapto sulfur atom of the foregoing compoundsto produce compounds such as 3-amino propanethiolethane and 1,3-diaminopropanethiolmethane.

In order to illustrate the use of some typical mercapto amines inpreparing the reclaimed rubber of this invention the following specificexamples are set forth:

Example 1.-l000 grams of ground grey inn-er tube scrap are heated with50 grams of tri-isopropanethiol amine in an autoclave at 370 F. for 24hours. At the end of this period the plastic mass is removed from theautoclave, cooled, washed on a corrugated roll mill and sheeted.

Example 2.90 pounds of ground rubber tire tread scrap are heated with4.5 pounds of 2- amino 2-methyl propanedithiol-l,3 in a No. 3 Banburymixer. Steam at 400 F. is admitted to the jacket of the mixer and thebatch is milled until the temperature of the batch reaches 400 F. Thisusually takes about 30 minutes. At the end of this period the plasticmass is removed, cooled and sheeted on a roll mill.

Example 3.-1000 grams of ground rubber tire tread scrap are mixed with50 grams of 2-amino ethanethiol and 50 grams of water. The mixture isheated in a steam jacketed vessel with steam at 397 F. for hours. At theend of this period the plastic mass is removed, cooled, run through acorrugated roll mill and dried.

As will be apparent from the several specific examples hereinabove setforth and as has been previously indicated, the mixture ofsoft-vulcanized rubber and reclaiming agent ordinarily should be heatedfor a time and at a temperature of the same order as the times andtemperatures customarily employed in the acid and alkali reclaimingprocesses. Heating is definitely essential to the present invention butthe heating conditions are subject to considerable variation as is truein the conventional reclaiming processes. In ordinary commercialmanufacturing operations, the heating period may vary from twentyminutes to twenty-four hours or even longer, while the temperatures mayvary from 200 F. to around 450 F., or even higher, so long as thetemperature-is not sufficiently high to decompose the materials; thehigher temperatures ordinarily being employed-for shorter periodsandlower tempera- .tures forlonger periods. In an" instances, the

heating should be continued until'the rubber is reduced to a plasticcondition, which will be readily recognized by a worker familiar withreclaiming processes.

The herein described invention is applicable to any of the various typesof soft-vulcanized rubber such as rubber scrap from boots, shoes, tires,inner tubes, belts, hose, and the like. Such scrap rubber may or may notbe freed from fibrous material such as cord and fabric reinforcementsand should preferably be comminuted.

The subject matter herein disclosed is also disclosed and claimedbroadly in my co-pending application Serial No. 302,366, filedconcurrently with this application on Nov. 1, 1939.

Having herein disclosed and described illustrative embodiments of myinvention it is my desire that the invention be not limited to theseembodiments but rather protected broadly, as limited only by the spiritand scope of the appended claims.

I claim:

1. A'method of reclaimingsoft vulcanized rubber which comprises"associating the vulcanized rubber with an aliphatic mercapto aminehaving the general formula wherein R is an. aliphatic nucleus; X is amember of the. class consisting of hydrogen atoms, by drocarbon nuclei,.and substituted hydrocarbon nuclei containing as substituents onlymembers of the class consisting of hydroxyl groups, mercapto groups andamino groups; Y is a member of the class consisting of hydrogen atoms,hydroxyl groups,'hydrocarbon nuclei, and substituted hydrocarbon nucleicontaining as substituents only membersof the class consisting ofhydroxyl groups, mercapto 1 groups, and amino groups; A is a radicalincluding a mercapto sulfur atom attacheddirectly to R and'in which theremaining valence 'of 'the mercapto sulfur atom is satisfied by a memberof. the class consisting of hydrogenatoms and. hydrocarbon nuclei; andheating the associatedmaterials at a temperature not lower than 200 B.until vthe'rubber becomes plastic.

2. A method of reclaiming soft-vulcanized rubber which comprisesassociating. .the vulcanized rubberwith an alkanemonothiol. amine, andheating the associated materials ata-temperature not lower than 200" 1.Faiuntil the rubber becomes plastic.

' 3. A method of-reclaiming soft-vulcanized rubber which comprisesassociating the vulcanized rubber with an ethanethiol' amine,.and'heating the associated materials until the rubber becomes plastic at atemperature not lower than 200 F.

A. A method of reclaiming soft-vulcanized rubber whichcomprises-associating the vulcanized rubber with Z-amino ethanethiol,and heating the associated materials at a temperaturenot lower than 200F. until the rubber becomes plastic.

'5. A method of reclaiming soft-vulcanized rubber'whichcomprisesassociating the vulcanized rubberwith apropanethiol amine, andheating the associated materials at a temperature not lower than 200 F..until the rubber becomes plastic.

6. A method of reclaiming soft-vulcanized rubberwhich comprisesassociating the vulcanized rubber with 1,3-diamino propanethiol,ancLheat- 'ing the associated materials at a rtemperaturernot lower than200 F. until the rubber becomes plastic.

7. A method of reclaiming soft-vulcanized rubber which comprisesassociating the vulcanized rubber with an alkanedithiol amine, andheating the associated materials 'at a temperature not lower than 200 F.until the rubber becomes plastic.

8. A method of reclaiming soft-vulcanized rubber which comprisesassociating the vulcanized rubber with a propanedithiol amine, andheating the associated materials at a temperature not lower than 200 F.until the rubber becomes plastic.

9. A method of reclaiming soft-vulcanized rubber which comprisesassociating the vulcanized rubber with 2-amino 2-methyl propanedithiol-1,3, and heating the associated materials at a temperature not lowerthan 200 F. until the rubber becomes plastic.

10. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of an aliphatic mercapto amine having the general formula A-R-Nwherein R is an aliphatic nucleus; X is a memgroups; A is a radicalincluding a mercapto sulfur atom attached directly to R and in whichtheremaining valence of the mercapto sulfur atom is satisfied by amember of the class consisting of hydrogen atoms and hydrocarbon nuclei.

11. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of an alkanemonothiol amine.

12. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of an ethanethiol amine.

13. A plastic reclaimed rubber that has'been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of 2-amino ethanethiol.

14. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of a propanethiol amine.

15. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of 1,3-diamino propanethiol.

16. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and inthe.

presence of an alkanedithiol amine.

1'7. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of a propanedithiol amine.

18. A plastic reclaimed rubber that has been prepared by heatingsoft-vulcanized rubber at a temperature not lower than 200 F. and in thepresence of 2-amino 2-methyl propanedithiol-1,3.

PAUL J. DASHER.

